In the production of a spun-bond web, filaments are extruded from a spinneret, are cooled and are aerodynamically stretched beneath the spinneret and are deposited upon a continuously movable collection or deposit belt which is foraminous or in the form of a screen so that the jumble of filaments can form a mat or fleece which passes beneath a pressing roller or between a pair of pressing rollers as the web is carried along in the direction of displacement of the continuously movable belt. Beneath the belt or screen a suction device is provided for drawing air through the belt to facilitate the deposition of the filaments on the belt to form the web.
As a practical matter, the filaments emerge from orifices of the spinneret and initially traverse a cooling chamber or passage in which those filaments are subjected to contact with process air for the cooling of the filaments before passing into a stretching unit which has, at its lower end or outlet side, a drafting channel exercising the aerodynamic entrainment upon the filaments to stretch the latter.
Then, preferably, the filaments pass via at least one diffuser forming part of a tiering unit which layers the filaments onto the screen.
The screen itself is an endless circulating outlet and the suction device below it draws the air through the belt and reliably pulls the filaments onto the belt and reliably holds the fleece which is formed against the belt. Downstream of the collection zone, the pressing rollers are provided to press the web against the belt or between the rollers located above the web and below the belt where a pair of such rollers is provided.
In general, such apparatus has been found to be highly effective with respect to the production of spun bond, but to permit improvement especially with respect to the uniformity of the deposition of the filaments and the formation of the fleece. In some cases with the conventional apparatus, nonhomogeneities with respect to filament density and the fleece mesh width or porosity can arise and can lead to variations in the properties of the web such as strength, elongation, permeability or the like.